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Computer Interfacing and Peripheral Equipment Laboratory Report (Rick L. Swenson)
Laboratory exercise number:
Practice 14.
Laboratory exercise name: Thyristors and solid state interfacing.
Name: Roll Number Date
Martn Santiago Francisco 01202208 April- 10-2013
Giovanni De la Vega Huerta 01204102
Israel Pimentel Bermdez 01204459
Material:
LM339 Quad Voltage Comparator (for single power supply)
Unijunction Transistors (UJT): 2N2646
Silicon Controlled Rectifiers (SCR): TIC106B or C106D
TRIACs: 2N6073 or Q4010
OptoIsolators: MOC3010
Light Bulb (Resistive Load)
Hair Dryer (Inductive Load)
Several Resistors of different values (see schematics)
1 NPN transistor 2N2222A
Monostable multivibrators: 74LS221
Report description:
Thyristors are typically used for power electronics interfacing and control. During
this laboratory experiment you will be using three of these devices, namely: SCRs, UJTs
and TRIACs.
Obtained results with schematic, block diagrams and timing diagrams:
Stage 1. SCR applications
Assemble the following two circuits shown in Figure 1. If you cant find a 6V light bulb, use a 330 Ohms resistor with a LED connected in series. For RL, also use a LED.
Figure 1: SCR application examples
Figure 2: Figure 3: Circuit implemented on
breadboard
Stage 2. TRIAC applications
The following circuit (Figure 4) is for switching resistive loads (e.g. light bulb, heater
element, etc.) connected to an AC source using digital circuitry. It uses a MOC3010 to
provide optical isolation between the digital circuitry and the AC source. For the resistive
load, RL, use a 60 Watt light bulb.
Figure 4: Digital circuitry interfaced to an AC resistive load
Figure 5: Figure 6:
The following circuit (Figure 7) is for switching inductive loads (e.g. motors) connected
to an AC source using digital circuitry. It uses a MOC3010 to provide optical isolation
between the digital circuitry and the AC source. For the resistive load, ZL, use a hair dryer
motor.
Figure 7: Digital circuitry interfaced to an AC inductive load
Figure 7: Digital circuitry interfaced to an AC inductive load on protoboard.
Stage 3. UJT applications
Figure 8 shows two oscillators using and UJT. Assemble both circuits and verify that the
LED flashes for the circuit on the left. Then check that a varying tone is heard on the
speaker when you turn R2.
Figure 8: UJT oscillator circuit
Figure 8: Time base implemented on
protoboard.
Figure 9: Tone generator implemented
on protoboard.
A ramp generator based on an UJT is depicted in Figure 10. Verify the functionality of
the circuit by putting it together. Connect an oscilloscope to the output OUT.
Figure 10: UJT ramp generator circuit
Figure 11: UJT ramp generator circuit
implemented on protoboard.
Figure 12: Output of the circuit.
Stage 4. Challenge
In this section, we decided to solve the challenge 1 that is the next:
Challenge 1: Modify the digital side of Figure 2, to convert the circuit into a light dimmer. In order to achieve this, you will have to use a monostable multivibrator
(74LS221) and a zero-crossing circuit to detect when the AC voltage crosses 0V.
The zero-crossing circuit is shown in Figure 13.
Figure 13: zero-crossing circuit used to detect when a 120VAC phase crosses 0V
generating square wave pulses.
This circuit is directly coupled to the AC line and it is only recommended as a temporary way of checking zero-crossing. Be very CAUTIOS with the top circuit and dont use it a permanent solution.
Next we present the circuit results.
In these images we can observe how the light intensity changes according to the value of
resistor, implemented with a potentiometer, so we can assume that the triack its working
according to the requirements of the challenge.
In these images we compare the output signal from the monostable multivibrator with the
voltage level that receives the load, in order to observe how the alternate voltage input its cut by
the tirack, and how this action modulate the intensity light of the bulb.
Conclusions:
1. We learned that an input gate signal causes the SCR to turn on, allowing forward current conduction. SCRs are true rectifiers: they only allow current through them
in one direction. This means they cannot be used alone for full-wave AC power
control.
2. Also we learned that the unijunction transistor are used for a wide range of applications such as sawtooth generators, trigger circuits, timing controls and
other related circuits.
Problems encountered:
1. We did not find an AC motor to test the proper operation of the digital circuitry interfaced to an AC inductive load.